Metamagnetic transitions induced by doping with non-magnetic 4+ ions in ludwigites Co5A(O2BO3)2 (A=Zr and Hf)

Abstract

The novel A-doped Co3O2BO3 (A4+=Zr, Hf) ludwigites have been synthetized by the first time and investigated by X-ray diffraction, magnetization and specific heat experiments. The non-magnetic ions place mainly at sites 4 of the structure. This doping strengthens the magnetic interactions rising the magnetic transition temperatures from 42 K, for the undoped compound, to 71 K and 72 K for Zr and Hf, respectively. These magnetic transition temperature are ~ 10 K below that shown by the Sn4+-doped Co3O2BO3. As expected, all these isostructural and isovalent compounds exhibit the same magnetic features. However, low temperature specific heat experiments and magnetization curves with typical metamagnetic behavior revealed that doping with the non-magnetic open-shell ions d0 Zr and Hf preserves the two-dimensional antiferromagnetic character of the parent ludwigite Co3O2BO3 while the closed-shell d10 Sn leads to a three-dimensional magnetism. The experimental results are compatible with an antiferromagnetic structure with a ferromagnetic component for these two compounds. The difference in TN and dimensionality of these compounds are related to super-superexchange (SSE) interaction between two Co2+ mediated by the non-magnetic ion A4+. The non-magnetic closed-shell d10 ion turned out to be more effective in mediating SSE interactions between 1−2−3 magnetic layers.